DUST: Public enemy number one!

                                                           Dust Public Enemy Number One

Coal Dust!

When material falls or is blown from conveyors or is stripped from dockside stockpiles by the wind, that's profit falling out of the operation. Worse still, the material that's lost is likely fall to earth somewhere from where it can come back to haunt you in the form of increased costs in a number of ways, such as by hastening the need for maintenance, fines from the authorities, Environment Agency enforcement notices or even 'stop' notices.

In some countries site owners and operators are required to take whatever steps are necessary to minimise the impact of operations on their surroundings. In others, like China, which have traditionally had a more relaxed attitude to such issues, there is an awakening that standards have to change, and that's reflected in the plans for new developments like the Qinhuangdao Port.

It's China's biggest coal transhipment port, and had a throughput of 200m tonnes last year. By 2015, by when its throughput is expected to have doubled, the port is predicted to have spent more than $127m on environmental protection.

Defining dust as particles emitted to air that constitute visual, physical, chemical or health hazards for employees or the public offers a feel for the importance of the issue to anyone moving dust-generating material.

The actual transfer of material from ship-to-shore and vice-versa is well catered for and controlled by the sophisticated filtration systems in use, but these often fail to extend as far as stockpiles or road and rail vehicles during other parts of a load's journey.

The most common sources of dust in the port industry are therefore the same as many others - any open storage, handling and spillages of dry bulk cargoes.

And port operators can be at the wrong end of it because of the physical properties of some bulk cargoes. The brittleness of coal, for example, means that repeated handling causes it to break into ever finer and finer pieces, simultaneously increasing the potential for dispersal on lighter and lighter winds.

Particles smaller than 10 microns can cause respiratory problems for employees. Larger particles need to be controlled because of their economic value, their visual and environmental impact, and their influence on maintenance frequency.

Canadian company Weathersolve Structures has done considerable research into the way material of varying sizes is moved. Movement can be caused by winds of varying speeds and by mechanical influences, including falling from a conveyor, being disturbed by conveyor transfers or discharges, or by vehicle tyres.

In all cases, says the company's design engineer Mike Robinson, the distance particles move each day depends on the vagaries of the wind and the size and weight of the particle. The lightest, smallest dust particles can get caught in wind up draughts like a glider, and can be carried thousands of miles as a result. Larger particles will be blown a distance as they fall from a conveyor.

"After they hit the ground they then move along the ground in a skipping motion (like a rock thrown across the surface of a pond). The movement across the ground (called saltation) depends on the wind speed, the roughness of the ground and the size and weight of the particle," says Mr Robinson.

"Particles too heavy to saltate in a given wind may still be moving by rolling. As the wind speed increases, larger and larger particles begin moving, and the smaller, saltating particles start getting lifted into the general airflow.

So how can dust be brought under control? Putting stockpiles inside is one solution, but is not always practical.

Windbreaks can be another answer, and that's the one promoted by Weathersolve. With expertise built over 20 years developing windbreak and fencing technology to protect kiwi fruit from the worst of the weather on behalf of New Zealand's Ministry of Agriculture, Mr Robinson is an expert in porous fabric structures.

He says a windbreak can reduce the speed of the incoming wind, and its ability to pick up the material being protected, by three quarters; if the windbreak is 50 feet high, then the reduced wind speed area will extend for about 250 feet downwind. For 250 feet beyond that, the wind will be half that of the incoming wind. Taller windbreaks will naturally create larger wind shadows.

Trees can form an effective windbreak, but can take far too long to grown to an effective size. They nevertheless share the benefit of porous fabric structures in that air can pass through them, and in doing so act as a buffer to prevent the air that flowed over the top crashing down on the material being protected.

But slowing the wind is only part of the story. Still more control can be achieved by the application of water and dust suppression agents, each with a specific role.

Identifying which one will suit your site is a matter for experts, but they fall into broad categories, such as open areas and stockpiles, roadways and smaller handling yards, loading bays and vehicle exit points.

With ever-tightening environmental controls, particularly in Europe, it remain clear that more positive steps will continue to be required to keep ahead of the legislation, probably involving several methods of control for each material with the potential to be turned into dust on its journey through a port's handling and storage systems.

Unprotected areas open to dust erosion

Protected stockpile

If you’re under of pressure to find solutions for dust control problems – in addition to all the other pressures you face – you might want to consider the unique advantages of WeatherSolve wind shelters. 

WeatherSolve wind shelters can be designed to heights of 100 feet (30 meters) for greater control of dust over larger areas. With poles up to 120 feet apart (36 meters) they also make it easy to accommodate conveyors and buildings and to cross roadways. They can even include doors for trucks to pass through. 

Of course, the requirement for fewer poles also means lower structural costs and far less disruption during construction. Self-cleaning, and needing no daily consumables like oil, gas, electricity or water, WeatherSolve wind shelters are exceedingly low maintenance. 

WeatherSolve designs have been thoroughly proven in every extreme from Hurricane Andrew (Florida 1992) and South Pacific cyclones to the unrelenting heat of Oman and Bahrain, the severe cold of Canadian winters in Northern B.C. and the South American Andes at 16,000 feet. We know of no other company anywhere near close to such experience. 

Worldwide, total area under WeatherSolve protection exceeds 1,000 acres. 

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